Method for the gasification of biomass-comprising material and installation therefor The present invention relates to a method for the gasification of biomass-comprising material in the pres- ence of an oxygen-comprising gas in a gasification instal- lation, during which gasification a hot gasification pro- ducts-comprising gas is formed, which installation com- prises a gasification chamber provided with an inlet open- ing for the supply of biomass, means for cooling the hot gasification products-comprising gas and for using the released heat to heat the oxygen-comprising gas before its introduction into the gasification chamber, for which pur- pose the installation is provided with a first opening and a second opening for the supply and discharge of gas, and oxygen-comprising gas is alternatingly supplied via a first opening, and gasification products-comprising gas is discharged via a second opening, and vice versa.

Such a method has been known in the field since the seventies as the Andco Torrax-process. More specifically, this method entails the introduction of the biomass-con- taining waste from the top into an elongated cylindrical and vertically positioned gasification chamber, the intro- duction at the bottom, of oxygen-comprising gas, in a direction opposite to the supply direction of biomass-com- prising waste, and the discharge at the top of hot gasifi- cation products-comprising gas. A portion of this hot gas is alternatingly supplied to one of two regeneration towers to which it gives off heat. The other of the two regeneration towers is alternatingly supplied with air.

The air moves through the regeneration tower in a direc- tion opposite to that of the gasification products-compri- sing gas previously supplied through said regeneration tower. The bottom of the gasification chamber is provided with an opening'for the discharge of liquid slag.

The object of the invention is to improve the known method and in particular to avoid the use of a costly, high temperature-resistant shuttle valve. It is a further

objective to provide a method allowing the biomass to be supplied at a point in the installation where the prevail- ing temperatures are relatively low.

According to the present invention the objective is attained by employing as installation a reverse-flow reac- tor comprising two packed beds between which there is a space serving as gasification chamber, the reverse-flow reactor being provided with the first and the second open- ing, and the line of direction in which the gas supply passes through the biomass cuts the line of direction in which the biomass is supplied.

A reverse-flow reactor is generally known in the field, for example from the American patent publication No. 2,700,600. The direction of the gas movement prevents hot gas coming into the vicinity of the supply opening for biomass. The efficient recovery of heat with the aid of a reverse-flow reactor renders high-temperature gasification attractive in terms of energy. Due to the high tempera- ture, biomass with a relatively high water content is also pre-eminently suited for gasification, thereby lowering, or even avoiding, the costs for a drying step. Any tar products and soot particles formed and deposited in the packed bed will, due to the high temperature in the pres- ence of oxygen from the oxygen-comprising gas, be combusted as soon as the gas flow is reversed again. An important advantage of the method according to the inven- tion over the method of the prior art is the more favour- able composition of the decomposition products. For example, fewer tar-like products are formed, making it easier to utilize or refine the gasification products-com- prising gas. Besides, with the prior art method, the biomass is pre-dried by the hot decomposition gasses and much water ends up in the hot gasses. With the present invention said drying occurs to a lesser extent, so that more water is present during pyrolysis, resulting in a relatively greater production of hydrogen.

According to a favourable embodiment the biomass is supplied at an angle of substantially 90°.

This provides a symmetrical distribution of biomass that has undergone partial pyrolysis in the gasification chamber, which is conducive for continuous operation of an installation at constant processing conditions.

According to a further favourable embodiment, the biomass is supplied via a tapered inlet opening.

In this manner problems relating to the transport of biomass to the gasification chamber are largely avoided.

Finally, the invention relates to an installation for the gasification of biomass-comprising material, which installation comprises a reverse-flow reactor having a first chamber for a first packed bed and a second space for a second packed bed, between the first and the second chamber a gasification space is provided, the end of the first chamber opposite to the gasification chamber is pro- vided with a first opening and the end of the second cham- ber opposite to the gasification space is provided with a second opening, the gasification space is provided with a third opening for the supply of biomass-comprising material, and the bottom of the gasification space is pro- vided with a fourth opening for the discharge of slag, the walls of the chambers and the space being formed from fireproof concrete.

The construction of such an installation is rela- tively inexpensive and joints that could exhibit leakage resulting from temperature fluctuations, are largely avoided. All the connections of tubes to the first and second openings are relatively cold openings.

The invention will now be explained with reference to the drawing, in which the only figure represents a cross-sectional view of an embodiment of a suitable installation for working the method according to the invention.

The figure shows a reverse-flow reactor 1 compris- ing two packed beds 2,3 and a gasification chamber 4. At each end the reverse-flow reactor 1 is provided with open- ings 5,6 for the supply or discharge of gas, as will be explained below. Biomass such as, for example, grass from

verges, elephant grass and wood chippings from willow and poplar are supplied via a tapered tube, reaching the gasification chamber via opening 8.

Via a tube 9 and a shuttle valve 10 in a first position, an oxygen-comprising gas such as air is supplied to opening 5. The air is heated in the packed bed 2 and is introduced into the gasification chamber 4. A small amount of oxygen is supplied, and the heat produced during the reaction of oxygen with biomass or its pyrolysis products, effectuates gasification of the biomass. In this manner a hot gasification products-comprising stream is formed which is discharged via the packed bed 3. In the packed bed 3, the hot gasification products-comprising stream gives off heat to the bed material. Via a shuttle valve 11 in a first position, the gasification products-comprising gas is discharged through discharge pipe 12. The gas may be utilized for all kinds of purposes, such as for syn- thesis purposes or for the generation of electricity.

When the down-stream end of the packed bed 2 is becoming so cold that the oxygen-comprising gas is no longer heated sufficiently, or the down-stream end of the packed bed 3 is becoming so hot that the gasification pro- ducts-comprising gas is no longer cooled sufficiently, the shuttle valves 10,11 are switched to a second position, reversing the flow direction through the reverse-flow reactor. This results in the packed bed 3 being cooled again and the packed bed 2 being heated. In this way the heat remains to a large extent inside the installation and the biomass can be gasified at high temperature in a man- ner favourable with respect to energy.

For starting the installation, the oxygen supply to the biomass may temporarily be increased so that more biomass is incinerated and more heat develops. Alterna- tively, a packed bed may first be heated electrically.

As is known in the field, the packed beds may com- prise, for example, alumina granules having a size of, say 5 mm. They may also comprise catalyst granules. These will then be located substantially in a zone in the packed bed where temperatures occur that are high enough to catalyze

the reaction, but not so high that the catalytic activity of the catalyst granules is destroyed.

Since the mol stream of hot gasification products- comprising gas is larger than the mol stream of oxygen- comprising gas, the packed beds 2,3 have to be cooled (not shown). This is done to advantage in a direction opposite to the heat gradient, so that, for example, hot steam may be obtained for the generation of electricity or for the production of processing heat.

Instead of cooling, it is also possible to dis- charge a part of the hot gas from the gasification chamber 4, or optionally also from a hot part of the packed bed 2,3.

Advantageously the oxygen-comprising gas supplied to the reverse-flow reactor 1 is oxygen-enriched air or substantially pure oxygen. In this manner it is possible to obtain a gasification products-comprising gas of a higher caloric value.

According to an interesting embodiment, the axis of the supply opening for biomass is substantially horizon- tal.

This prevents that due to diffusion hot vapours already start the pyrolysis process of the biomass, and that tar formation impedes the transport of biomass.

As known in the field, the liquid slag may, via a slag discharge opening 13 which in this case is embodied as overflow, be quenched in cold water. This effectively immobilizes harmful heavy metals that may be present.

All parts of the installation that are likely to be exposed to much increased temperatures are, as is known in the field, manufactured from fireproof materials of the kind used, for example, in blast furnaces. Apart from ceramic materials, fireproof concrete is a material that according to the invention in particular comes to mind.

Such an installation can be cast in accordance with known techniques, and comprises only a limited number of parts.

As a consequence the number of joints is also limited.

Accordingly, as represented in the Figure, the top of the installation could, for example, be a lid. The resulting

gap between the lid and the installation underneath can simply, in a manner known in itself, be sealed, which sealing will be maintained even at fluctuations tempera- tures.

In a manner known as such, the installation is suitably insulated and may also be provided with insula- tion material on the outside. The shaded part in the fig- ure represents the insulation material. A suitable insula- tion and sealing material is alumina-silica fibre-compris- ing insulation material.

At the high temperatures in the gasification cham- ber 4, tar-like products that may be present are gaseous.

When they are passed through a bed 2 or 3, they may pre- cipitate, which is undesirable. According to a favourable embodiment oxygen, for example in the form of air, is sup- plied to the gasification chamber 4 and this should pre- ferably always be above the bed via which the gasification products-comprising gas is discharged. In this manner the deposition of tar-like products in the beds is prevented efficiently and economically.